1. Field of the Invention
The present invention relates to a pixel circuit having a light emitting element, an image display apparatus and a driving method thereof. The present invention also relates to a driving method of an electronic device.
2. Description of the Related Art
Recently, many researchers have focused attention on electroluminescent elements (hereinafter also referred to as “light emitting elements”). In particular, studies on the application of the light emitting elements to image display apparatuses or lighting apparatuses have been actively carried out.
The above-described image display apparatuses include pixels at least including the light emitting elements and thin film transistors (hereinafter abbreviated as “TFTs”) made of amorphous silicon, polycrystalline silicon, or the like. Control of the TFTs allows a desired current to flow through the light emitting elements, and the brightness, hue, saturation, or the like of the pixels are appropriately controlled.
It is known that a threshold voltage (hereinafter also referred to as a “Vth”) of a TFT made of amorphous silicon (hereinafter also referred to as an “aSi-TFT”) increases with time of using the TFT to cause a change in operating conditions. This phenomenon is called “Vth shift” or “deterioration” of the aSi-TFT. It is also known that the aSi-TFT provides a large change in the rate of deterioration depending on the use thereof, operating conditions, etc.
For example, in applications for which an aSi-TFT is used as a switch and a pulsed current flows through the aSi-TFT for a very short time, such as liquid crystal displays, the rate of deterioration of the aSi-TFT is low. On the other hand, in applications for which a large current flows through the aSi-TFT, such as organic light emitting elements, the rate of deterioration of the aSi-TFT is high.
Deterioration of aSi-TFTs affects the uniformity of an image and the response of pixels.
There is a circuit technique called Vth correction. This is a technique in which a Vth of an aSi-TFT is detected and a video signal is superimposed on the Vth to provide a uniform image regardless of the deterioration of the Vth of the aSi-TFT.
A Vth correction technique of the related art is described in, for example, S. Ono et al., Proceedings of IDW '03, 255 (2003). This document discloses a Vth correction technique performed by an image display apparatus using four TFTs and four control lines. The contents of this publication are incorporated herein by reference in their entirety.